The invention is related to the field of hearing aids, and in particular, to a hearing aid that includes an implantable acoustic transducer for providing acoustic signals into the middle ear cavity of a patient.
Implantable hearing aids entail the subcutaneous positioning of some or all of various hearing augmentation componentry on or within a patient""s skull, typically at locations proximal to the mastoid process. In a semi-implantable hearing aid, a microphone, signal processor, and transmitter may be externally located to receive, process, and inductively transmit a processed audio signal to an implanted receiver, while a transducer is implanted within the patient. Fully-implantable hearing aids locate the microphone, transducer, and signal processor subcutaneously. In either arrangement, a processed audio drive signal is provided to some form of actuator to stimulate a component of the auditory system, typically the ossicular chain, within the middle ear of a patient. In turn, the ossicular chain stimulates the cochlea to cause the sensation of sound in a patient.
By way of example, one type of implantable actuator includes an electromechanical transducer having a magnetic coil that drives a vibratory member positioned to mechanically stimulate the ossicular chain via physical engagement. (See e.g. U.S. Pat. No. 5,702,342). In this regard, one or more bones of the ossicular chain are made to mechanically vibrate, causing the vibration to stimulate the cochlea through its natural input, the so-called oval window. An example of such a transducer is included in the MET(trademark) hearing aid of Otologics, LLC, developed by Fredrickson et al in which a small electromechanical transducer is used to vibrate the incus (the 2nd of the 3 bones forming the ossicies), and thence produce the perception of sound.
In another example, implanted excitation coils may be employed to electromagnetically stimulate magnets affixed within the middle ear. In each of these approaches, a changing magnetic field is employed to induce vibration. While these devices significantly improve over other devices, they still include at least one surgically achieved contact interface or mechanically fixed point with a component of the middle ear. Such mechanically fixed points may be subject to environmental pressure changes and other conditions, and therefore, are not ideal for all hearing impaired individuals. In this regard, it is desirable in the art of hearing aids to enhance the sensation of sound in hearing impaired individuals so that such individuals may have normal or very close to normal hearing function with the least amount of modification or connection of foreign devices to the auditory system.
In view of the foregoing, a primary object of the present invention is to provide an implanted hearing aid (either semi or fully implantable) in a manner that entails reduced surgical procedures and contact with the auditory system. Another object of the present invention is to provide a hearing aid that may be fitted on a patient-by-patient basis in an efficient manner.
In this regard, the present inventor has realized the desirability of a hearing aid device that utilizes an implantable acoustic transducer to stimulate the tympanic membrane of a patient, in a contact-free manner, for instance via input of acoustic signals or vibrations into the middle ear cavity. Further, in this regard, the present inventor has realized the desirability of acoustically coupling the tympanic membrane and the acoustic transducer to efficiently provide the acoustic stimulation of the tympanic membrane and thereby generate the sensation of sound using the natural mechanical advantage provided by the ossicular chain.
In carrying out the above objects of the present invention, the present inventor has further recognized that the impedance of an implanted acoustic transducer may be matched to a characteristic acoustic impedance range for human tympanic membranes to acoustically couple the transducer with a tympanic membrane. By matching the impedance of the transducer to that of the human tympanic membrane, the transducer acoustically couples for the transmission of acoustic signals with the tympanic membrane due to the impedance difference between the tympanic membrane, having relatively low impedance, and the other components of the middle ear, having relatively high impedance.
In other words, because significantly more power is required to stimulate the other components, namely, the oval window, round window, and ossicular chain, than is required for tympanic membrane stimulation, the impendence matching effectively forms an acoustic coupling with the tympanic membrane. This in turn permits the introduction of acoustic signals, generally into the middle ear cavity of a patient, that stimulates the tympanic membrane without stimulation of other components of the middle ear cavity, other than through the natural stimulation provided by the tympanic membrane (e.g. in response to stimulation by the acoustic signals the tympanic membrane stimulates the ossicular chain which in turn stimulates the cochlea to produce the sensation of sound).
In view of the foregoing, a first aspect of the present invention includes a method entailing the step of matching the impedance of an acoustic transducer to a predetermined characteristic impedance range for human tympanic membranes. The method further includes implanting the transducer proximate to the middle ear cavity of the patient and providing acoustic signals to the middle ear cavity in response to transducer drive signals. The transducer drive signals being generated in response to acoustic sound received at an acoustic signal receiver (e.g. a microphone).
In this regard, the transducer may be implanted substantially adjacent to the middle ear cavity so that the transducer may provide the acoustic signals generally into the middle ear cavity, such as, via an aperture formed therein. In the alternative, the transducer may be implanted within the mastoid process of the patient and an acoustic path provided between the transducer and the middle ear cavity. In the later case, the acoustic path may be a biocompatible tubing connected at a first end to the transducer and a distal end to the middle ear cavity, e.g. via an aperture formed therein. In some cases, the tubing may be extended slightly into the middle ear cavity to prevent occlusion caused by tissue growth over the interfacing end of the tubing. In another example, the interfacing end of the tubing may be formed at an angle to further deter occlusion caused by tissue growth. Similarly, other methods, such as disposing a sound transmitting material over the interfacing end of the tubing may also be utilized to prevent occlusion by tissue growth.
In a second aspect of the present invention, a method is provided that includes the steps of measuring an impedance of a patient""s tympanic membrane and matching the impedance of an acoustic transducer to the measured impedance of the patient""s tympanic membrane. In this regard, the method further includes, implanting the transducer proximate to the middle ear cavity of the patient and providing acoustic signals to the middle ear cavity in response to transducer drive signals. The transducer drive signals being generated in response to acoustic sound received at an acoustic signal receiver (e.g. a microphone).
As with the above-described method, the transducer may be implanted substantially adjacent to the middle ear cavity so that the transducer may provide the acoustic signals generally into the middle ear cavity, such as, via an aperture formed therein. In the alternative, the transducer may be implanted within the mastoid process of the patient and an acoustic path, e.g., biocompatible tubing, provided between the transducer and the middle ear cavity. The tubing may be extended slightly into the middle ear cavity and/or the interfacing end of the tubing formed at an angle to prevent occlusion caused by tissue growth. Similarly, other methods, such as disposing a sound transmitting material over the interfacing end of the tubing may also be utilized to prevent occlusion by tissue growth.
In a third aspect of the present invention, a method is provided that includes the steps of coupling an implantable transducer to a middle ear cavity of the patient. The coupling may include implanting the transducer substantially adjacent to the middle ear cavity so that the transducer may provide the acoustic signals generally into the middle ear cavity, such as, via an aperture formed therein. In the alternative, the transducer may be implanted within the mastoid process of the patient and an acoustic path, e.g., biocompatible tubing, provided between the transducer and the middle ear cavity. The tubing may be extended slightly into the middle ear cavity and/or the interfacing end of the tubing formed at an angle to prevent occlusion caused by tissue growth. Similarly, other methods, such as disposing a sound transmitting material over the interfacing end of the tubing may also be utilized to prevent occlusion by tissue growth.
The method further includes, receiving acoustic sound in an acoustic signal receiver and generating transducer drive signals in response to receiving the acoustic sound. In this regard, the method further includes, in the transducer, providing acoustic signals to a middle ear cavity of the patient in response to the acoustic drive signals and damping the acoustic signals to provide damped acoustic signals to the middle ear cavity of the patient. The damping step substantially removes resonant components of the acoustic signal so that the damped acoustic signal is substantially free from such resonant components thereby increasing the quality of hearing perception for the patient.
In a fourth aspect of the present invention, a method is provided that includes the steps of coupling an implantable transducer directly to a middle ear cavity of the patient. The method further includes receiving acoustic sound in an acoustic signal receiver and generating transducer drive signals in response to receiving the acoustic sound. In this regard, the method includes, in the transducer, providing acoustic signals to the middle ear cavity of the patient in response to the acoustic drive signals.
In accordance with this aspect of the invention, the transducer may include a substantially non-resonant coupling mechanism to introduce acoustic signals to the middle ear cavity of the patient that are substantially free of resonant components. The non-resonant coupling mechanism may be a compliant structure that is acoustically transparent. In other words, the non-resonant mechanism permits the introduction of the acoustic signals directly into the middle ear cavity of the patient to substantially eliminate the introduction of resonant components. Further, in this regard, the non-resonant coupling mechanism may be a substantially conformal wall that minimizes contamination of the transducer, but does not include other structure that introduces resonant components into the acoustic signals. In one example of the present aspect, the non-resonant coupling mechanism is a titanium diaphragm disposed on the transducer between the transducer and an aperture in the middle ear cavity of the patient.
In a fifth aspect of the present invention, a hearing aid having an acoustic signal receiver, a signal processor, and an implantable acoustic transducer is provided. In this regard, the impedance of the transducer is matched to the characteristic frequency range of the human tympanic membrane to acoustically couple the transducer and tympanic membrane. In the alternative, the impedance of the transducer may be matched to a measured impedance of an individual patient""s tympanic membrane to achieve the acoustic coupling.
The acoustic signal receiver is configured to receive acoustic sounds and generate frequency response signals for the signal processor. The signal processor, in turn, processes the frequency response signals to generate transducer drive signals for the transducer. The transducer, in response to the drive signals, generates acoustic signals that are introduced into the middle ear cavity of the patient to stimulate the tympanic membrane.
As with the above-described aspects, the transducer may be implanted adjacent to the middle ear cavity with access provided for the introduction of acoustic signals via an aperture formed therein. In the alternative, the transducer may be implanted within the mastoid process of the patient and an acoustic path provided, such as biocompatible tubing, for introduction of acoustic signals to the middle ear cavity. The tubing may also be extended slightly into the middle ear cavity and/or the interfacing end of the tubing formed at an angle to deter tissue growth. Similarly, other methods, such as disposing a sound transmitting material over the interfacing end of the tubing may also be utilized to prevent occlusion caused by tissue growth.
In a sixth aspect of the present invention, a hearing aid having an acoustic signal receiver, a signal processor, and an implantable acoustic transducer is provided. In this regard, the transducer is implanted substantially adjacent to the middle ear cavity of the patient to permit the direct introduction of acoustic signals into the middle ear cavity. In accordance with this aspect, the transducer may include a substantially non-resonant coupling mechanism as described above to introduce acoustic signals to the middle ear cavity of the patient that are substantially free of resonant components.
As with the above-described aspects, the acoustic signal receiver is configured to receive acoustic sounds and generate frequency response signals for the signal processor. The signal processor, in turn, processes the frequency response signals to generate transducer drive signals for the transducer.
In a seventh aspect of the present invention, a hearing aid having an acoustic signal receiver, a signal processor, and an implantable acoustic transducer is provided. In this regard, the hearing aid may include a damping element to substantially dampen resonant components of the acoustic signals. As with the above-described aspects, the transducer may be implanted adjacent to the middle ear cavity with access provided for the introduction of acoustic signals via an aperture formed therein. In the alternative, the transducer may be implanted within the mastoid process of the patient and an acoustic path provided, such as biocompatible tubing, for introduction of acoustic signals to the middle ear cavity. In the case where the transducer is implanted adjacent to the middle ear cavity, the damping element may be provided in the transducer or in the signal processor. In the case where the transducer is implanted within the mastoid process of the patient, and an acoustic path provided, the damping element may be included in either the transducer or the acoustic path.
The damping element may be any element that removes or substantially removes resonant components of the acoustic signal. In this characterization, the damping element may be in the form of a resistor that shapes the transducer drive signals to minimize vibration of the acoustic signals. In another example, the damping element may be in the form of a porous material, such as porous foam included in the transducer or the acoustic path. In another example, the damping element may be included in the transducer and include a sealing wall disposed in a chamber of the transducer that includes a sound transmitting orifice defined therein. In this characterization, the damping element may further include an isolating diaphragm disposed within the chamber between the acoustic path and the sealing wall to dampen resonant components in combination with the sealing wall.
As with the above-described aspects, the acoustic signal receiver is configured to receive acoustic sounds and generate frequency response signals for the signal processor. The signal processor, in turn, processes the frequency response signals to generate transducer drive signals for the transducer.
As will be further described below, the present invention may be utilized in conjunction with either fully or semi-implantable hearing aid devices. In semi-implantable hearing aid applications, acoustic sounds may be inductively coupled to the implanted transducer via an external transmitter and implanted receiver. In fully-implantable applications, the acoustic sounds may be received by an implanted acoustic signal receiver e.g. an omni-directional microphone, and provided to an implanted signal processor for generation of the transducer drive signals. Additional aspects, advantages and applications of the present invention will be apparent to those skilled in the art upon consideration of the following.